1. Field of the Invention
The present invention relates to an electric parking lock device having a drive force generating means for engagement and/or release of a parking lock pawl with and/or from a parking lock gear in response to a command from a parking command means.
2. Description of the Related Art
With a vehicle in which the power from an engine is transmitted to driving wheels via a torque converter or a vehicle designed to be driven with an electric motor, it is not possible to utilize internal friction of the engine for locking the driving wheels. To cope with this, for instance, Japanese Patent Unexamined Publication No. HEI 8-216844 proposes an electric parking lock device in which a parking lock pawl is provided for engagement with and/or release from a parking lock gear provided on an output shaft of a transmission, and in which the parking lock pawl is operated by an electric actuator so as to lock driving wheels when the vehicle is stopped.
However, it is common with the electric actuator to adopt a construction which does not permit reverse driving through utilization of a screw means for transforming rotational motion of a motor to linear motion or interposition of a speed reducer to make the number of revolutions of an output shaft coincide with the operational angle of a parking lock pawl. Although this obviates the necessity of any special means for retaining he parking lock pawl at a regulated position, it follows that where the motor gets out of operation due to reduction in voltage of a battery or failure of an electrical system while the parking lock pawl is in engagement with the parking lock gear, it becomes difficult to release the parking lock pawl from the parking lock gear. Although the device disclosed in the aforesaid Japanese patent unexamined publication is provided with a manual lock release means, since the release means is constructed such that rotation force is applied to a gear shaft of the speed reducer, the construction becomes very complicated and production cost tends to be increased.